From Bourron-Marlotte to Montigny-sur-Loing via the Rocher des Étroitures

Starting point and access: Bourron-Marlotte-Grez station.
- Transilien - Line R, on the section between Paris-Lyon and Montargis.
Take the only exit, on the side of track 2 (in the direction of Montargis to Paris). If arriving in the opposite direction (track 1), take the underpass at the rear of the train.

Red and white + green and white markings

(S) With your back to the station, follow the road to the right towards Bourron-Marlotte. Pass the entrance to the Château de Bourron. Cross the Chemin de l'Étang on the right-hand side, then the Rue des Petits Saules. Immediately afterwards, turn left into a one-way street (Rue Chevreuil, signposted further on). This will take you to the foot of the church.

No signposts

(1) Turn right and walk along the church on your left. Just before a crossroads, turn left onto Ruelle des Mathurins, which quickly becomes a gravel path. At the T-junction, turn right and then left onto the path. At the end of the path, continue along a street. At the end, turn left onto Rue Pasteur. At the crossroads, go straight ahead slightly uphill.

(2) At the corner of No. 38, turn right (forest barrier) onto a path along a fence. Follow this path marked with old sandstone boundary stones that used to mark the boundary of the Fontainebleau National Forest, ignoring all the paths on the left. Note the tennis courts on the right and continue to a crossroads (forest barrier on the right). Then turn left into a wide lane lined with a fence on the right-hand side.

(3) At the T-junction, turn left, go through a forest barrier (plot no. 564) and go up a sunken path. Then turn sharply right and then left before reaching a crossroads. Then follow the path to the right, heading north towards Route de Marlotte (ignore the^first vague path on the right). At the next crossroads, go straight ahead onto a discreet path, Route de la Grande Mare (plot no. 553). The path gives way to a trail that descends a steep slope. At the crossroads after a slight climb, turn right onto Route de la Grande Vallée. Go downhill and then continue straight ahead on flat ground. At a fork, turn left onto the wider path. Continue for several dozen metres until you reach a tree with a Blue Cross (visible to those walking in the opposite direction).

Blue markings + blue capital letters on some rocks (read the recommendations in the "Practical information" section)

(4) Then turn left onto a path and climb gently. Wind your way between the rocks, alternating between short ascents and descents. At the Carrefour des Naturalistes (not signposted on site), cross a wider path and continue straight ahead on a discreet path. You will come to a wide path near the Mare aux Fées.

(5) Follow trail no. 11 opposite and leave the pond on your left. Walk along a small fence (erosion control device) on your left, then wind your way between the rocks. Pass a small viewpoint, then walk along another small fence on your left. After another viewpoint dotted with small rocks, leave large boulders on your left. After rock X, descend. Don't miss a sharp left turn and, after rock V, turn right at an acute angle. Then pass at the foot of a hill on your left.

(6) Cross the road carefully and continue straight ahead on trail no. 11. At the immediate three-way junction, go straight ahead and, at the fork that follows, turn left. Climb a hillock, following a few switchbacks. At the top (rock U, bench), continue north on the marked trail through the ferns. Squeeze between the walls of rock T and immediately turn right. Continue uphill with a slope on your left. Ignore a path on your left (steep shortcut) and descend through the ferns. Turn left, note the arrival of the shortcut on your left and continue under the pine forest.

(7) Cross a sandy path (erosion control fences). Immediately cross another path (ignore the green and white markings) and continue straight ahead on the blue trail. At a T-junction, turn left and you will immediately come to a crossroads at the foot of a hill, with a small rock in the centre bearing a blue marker.

No markings

(8) Take the^first path on the left (ignore a steeper trail opposite and leave the blue trail on the right). Climb up and, at a fork, turn right at the foot of a dead tree trunk that is still standing. Climb up following the faint trail with a few switchbacks. At the top, veer left then turn right. Follow a well-marked path eastwards between the ferns. Reach a rock slab and step onto it (ignore two vague tracks descending on either side). Continue straight ahead to a viewpoint.

Blue markings + blue capital letters on some rocks (read the recommendations in the "Practical information" section).

Continue for a few dozen metres along the edge of the plateau, then descend to the left to reach the Béatrix Cave.

(9) With your back to the entrance to the cave (which is more of a large shelter), follow the path opposite, which winds its way downhill. At a fork, take the path on the right, which remains flat at first. Then continue downhill. Climb back up, passing at the foot of rocks O, N and M. Turn right and pass rocks L and K. Walk along blocks I and H on your right and make a long traverse, more or less level (rocks G and F). Pass through a rocky gorge (rock E). After boulder B, turn right and you will come to a crossroads (signpost).

(10) Turn right towards the Grande Vallée Forest House and follow the blue markings for another 30 metres or so.

No markings

Take the^first path on the left (ignore the markings that continue straight ahead). At the crossroads that immediately follows (plot no. 548), turn left onto Route du Languedoc. At a three-way junction, turn right onto Route du Haut Mont (plot no. 538).

(11) At the crossroads, turn left onto Route du Croc Marin. At the fork that appears shortly afterwards, follow Route du Roi de Pologne to the left. At the next fork, turn right onto Route de la Gravine and go downhill. At the crossroads, continue straight ahead on Route de la Gravine.

(12) At the crossroads at the boundary between plots no. 537 and 547, turn right onto Route des Carrières and go uphill. The path turns left and reaches a sort of pass. Go downhill and continue straight ahead (east-southeast). At the T-junction (plot no. 547), turn right.

Yellow markings (rare)

At the next junction, go straight ahead and leave the national forest (signs indicate that the woods are private and that you must not leave the paths). At the next junction, continue straight ahead, south then south-west. You will come to a small road and follow it to the right for about a hundred metres.

(13) At the crossroads, follow a path on the right (fire hydrant). On the right-hand side, pass a small reservoir and then a water tank. Go up a stony path. At a crossroads (chain on the right-hand side), go straight ahead and downhill. Further down, take the^first path on the left. Ignore the paths coming from the right and rejoin the tarmac road. Walk past the cemetery on your left and continue straight ahead.

No markings

(14) At the crossroads, turn left. At the stop sign, continue straight ahead and descend. At the foot of the railway viaduct, follow Avenue de la Gare to the right. Continue straight ahead on a slight incline and you will reach Montigny-sur-Loing station on your left (E).

To return home:
- Transilien - Line R, towards Paris-Lyon (direct access) or Montargis (take the underground passage).

Train timetables: consult the Transilien website.

For motorists:
Both stations are located on the same section of the R line: park in the car park of one of the two stations and make a return trip by train.

Hiking boots are required. Given the twists and turns in certain sections, the elevation gain is probably underestimated: allow for around 300 m.

No water sources identified along the route. Pizzeria opposite Montigny-sur-Loing station (E).

A 1:25,000 map is essential (at least the one accompanying this description) or a route to follow using the Visorando app.

Recommendations concerning the blue-marked trails:
- The Denecourt-Colinet trails, marked in blue, mostly follow paths that wind through the rocks. It is impossible to describe the multiple changes of direction and the description only provides the most important landmarks.
- Consequently, follow the markings closely, as they are dense and well maintained (thanks to the markers!). If you have not seen a marker for some time, do not hesitate to retrace your steps until you find the markings again.
- Markers can be found on three types of supports, at three different heights: (i) on tree trunks at eye level; (ii) on rocks, at the same height or lower; (iii) on the ground, on rocks that are flush with the surface.

Warning:
The section between (8) and (9) follows a poorly marked trail: a good sense of direction is required and tracking the route on a smartphone is a definite plus.

Hike completed by the author on 8 May 2022.

- Pleasant forest trails.
- Rock chaos between (4) and (10), with several beautiful viewpoints.
- Mare aux Fées (5).
- Grotte Béatrix (9).